It is almost the only prior art polysilane synthesis method to condensate dichlorosilane with the aid of metallic sodium. This method, however, has several problems including difficulty to control reaction, low yields of high molecular weight polysilanes, and formation of insoluble polymers.
The following polysilane synthesis methods were proposed to obviate these problems. (1) Polysilane is prepared by subjecting RSiH.sub.3 to dehydrogenation condensation with the aid of Cp.sub.2 MR.sub.2 type complex wherein M is Ti or Zr. See J. F. Harrod, ACS, Polym. Prepr., 28, 403 (1987). This method can produce polysilanes having a degree of polymerization of about 20, but fails to produce polysilanes having a higher degree of polymerization. (2) Another method is to prepare polysilane through anionic polymerization using masked disilene protected with biphenyl. See Sakurai et al., Proceedings of Japanese Chemical Society 56th Spring Meeting (1988), 1IVO3. This method is not suited for commercial manufacture since the starting material, masked disilene is difficult to synthesize. (3) An improvement in the conventional synthesis method was attempted by adding crown ethers. See Fujino et al., Proceedings of Japanese Chemical Society 56th Spring Meeting (1988), 1IVB1. The addition of crown ethers was effective in promoting the reaction, but the final yield of high molecular weight polysilane was little improved as compared with the conventional method.
Therefore, an object of the present invention is to provide a polysilane preparing method capable of readily producing high molecular weight polysilanes in high yields.